Facebook chief executive Mark Zuckerberg endured an hours-long grilling by dozens of U.S. senators Tuesday during which he repeatedly apologized and promised privacy reforms but also pointedly defended his company against the threat of new legislation.

Zuckerberg invoked Facebook’s unlikely journey — from a tiny start-up he co-founded in his Harvard dorm room 14 years ago to a social media behemoth — in explaining Facebook’s frequent privacy missteps and its failure to spot and defeat Russia’s aggressive campaign to manipulate American voters in 2016 and beyond.